Coaxial condenser crystal and method of making same



Aug. 27, 1946. F, L, sALlsBURy 2,406,405

COAXIAL coNDENsER CRYSTAL AND METHOD oF MAKING SAME Filed May 19, 1941 MMW INVENTOR. FRI-:Demers L sALlsBuRY 1MM/M HIS ATTORNEY .5

Patented Aug. 27, 1946 COAXIAL CONDENSER CRYSTAL AND METHOD OF MAKING SAME Frederick L. Salisbury, Hempstead Gardens, N. Y., assignor to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application May 19, 1941, Serial No. 394,239

8 Claims. (C1. Z50-31) This invention relates to mountings for crystals such as are used for rectiers or detectors, and to a method for making these mountings.

In the Well-known cats-whisker type of crystal mounting, the crystal is held in a conducting body which forms one terminal, and the second terminal, or cats-whisker is held against a sensitive spot on the crystal. It is not only diiiicult to nd a sensitive spot on the crystal suitable for use, but it has been exceedingly difcult or impossible in devices heretofore used to keep the cats-whisker in contact with such a spot. Mechanical vibration, temperature variations, change in humidity of surrounding atmosphere, oxidation of Wire, etc., all tend to impair this contact and hence the eciency and eilectiveness of the crystal.

It is an object of the present invention to provide an improved crystal mounting which is stable in operation and ln which the contact between crystal and cats-whisker is substantially not alected by vibration, moisture, temperature or other iniluences to which crystal contacts have heretofore been subject.

It is another object of this invention to provide an improved crystal mounting which is sealed from the atmosphere and is mechanically secure against vibration, thus being suitable for use under conditions of change in temperature, humidity, pressure and vibration, as, for example, are found on airplanes.

It is still another object to provide a crystal mounting in which the cats-Whisker is permanently sealed in place by a thermoplastic dielectric material having high eliciency at ultra high frequencies, thereby permitting the crystal to be satisfactorily used at such high frequencies.

It is a further object of this invention to provide a, novel method of manufacturing a, mounted crystal unit which makes it possible to manufacture such units in extremely small size and of high emciency, such as are necessary for use with ultra-high frequency circuits.-

A further object is to provide a useful mounting for a crystal which is easily adapted to be connected in a concentric transmission line circuit.

Another object is to provide a useful crystal mounting for use with a concentric transmission line system which has a distributed by-pass capacitance built into the crystal mounting.

Y Still another object is to provide a mounting for a crystal inside a section of concentric transmission line, whereby the crystal is electrically shielded from extraneous electric elds. v

Further objects and advantageswill become apparent in the following specication and drawing, wherein, l

Fig. 1 is a section along the axis or" a complete crystal mounting and adaptor for concentric transmission lines;

Fig. 2 is an enlarged fragmentary vieW of the crystal engaging tip of the cats-whisker;

Fig. 3 shows the testing and assembling device for the crystal mounting of Fig. 1; and

Figs. 4 to 6 diagrammatically show cathode ray tube indications under various conditions to explain the testing of the crystal in the device of Fig. 3. i

Fig. 1 shows the completely assembled crystal rectifier or detector. This is made of a holder I, of brass or any other conductive material, provided With a recess 3 of suitable diameter. A small outlet or bleeder hole 5 is provided from the outside of holder I to the bottom of recess 3. Apiece of crystal 'i having unidirectional conducting properties, such as Zincite, silicon, Carborundum, galeria, hertzite, molybdenum, etc., is forced into recess 3 so as to make good electrical and mechanical contact with the inner Walls of holder I. Before placing the crystal in position it may be tested, in the manner to b-e described beloW, to insure that a sensitive portion is placed facing the opening of recess 3.l

The holder I and crystal 'l are then heated together by any Suitable means, as by being placed on the surface of an electric iron. When hot, some thermoplastic substance 3' having good dielectric qualities at ultra-high frequencies of the order of 109 cycles per second, such as Various types of materials known as polystyrene, is placed Within the recess 3. It should be noted here that any thermoplastic material having electrical properties suited to the intended use of the crystal may be used. When properly heated, the thermoplastic material becomes semi-fluid and flows around the crystal 1. All air is forced out the bleeder hole 5 and the thermoplastic material thoroughly wets and surrounds the exposed surface of crystal l and lls holder l so that, after cooling, the crystal l is kept completely separated from and independent of all atmospheric influences.

While the thermoplastic material is still plastic, the cats-Whisker conductor 9 is placed roughly concentrically Within recess 3. The conductor 9 is shown in Fig. 2 as made of metal tubing, flattened at one end, which is formed with an oirset sharpened tip Il. The particular shape of the cats-Whisker 9 is convenient for applicants method of manufacture, as will be apparent, but any type of wire or other small conductor may be used.

The entire unit as thus far assembled is then placed in proper position on a cooling and mounting base I3 (Fig. 3). This position may be marked by any suitable means, such as by a recess as at I or a holding jig may be used. The unit is thereby held immediately under the roughly concentric with an adjusting member I1 which is adjustably held in a split clamp I9 and fastened therein by some means such as a screw 2l. Member I1 has a reduced portion 23 which fits snugly into the hollow portion of cats- Whisker conductor 9, which is thus held by member I1 roughly in a position coaxial 'with recess 3. Member I1 is then manipulated as by turning with clamp I9 loosened until `the c'ats Whisker 9 is in contact with an optimum sensitive spot on crystal 1, as indicated on 'the test device to be described below. The finding of the sensitive spot is aided by the ofi-setting of portion II of conductor 9, as this permits ra large part `of the outward facing surface of crystal 'I to be explored. After lsuch a sensitive 'spot has been found, clamp I9 is fastened to hold member I1 in position while the thermoplastic material cools and hardens. The cooling is expedited `by running cooling water through suitable passage means in metal base I3, as bypipe 2-5. The cats- Whisker '9 is thereby cast rigidly i-nto the proper position. If no sensitive spot 4is found before the thermoplastic materia-l hardens, the unit is removed and reheated and the process is repeated.

By the above method I .secure a fixed crystal unit with cats-whiske'r 9 firmly and permanently secured in piace. 'The contact between crystal 1 and cats-whisker 9 is completely sealed oit from the atmosphere, and good permanent contact is `secured to the crystal 1. The unit so Aobtained is found to be vextremely stable in its characteristics `over wide 'changes of con- 'dit-ions of use. It is especially iresist-ant to vibration, and is therefore very usefulon 4airplane installations.

After cooling, the base of crystal holder `I is placed in an adjustably eccentric "chuck Aof a lathe, while conductor 9, now a fixed part of the unit, is used to center the unit -in the lathe. The outside of Vholder lI is no'w turned Jdown lon the lathe to roughly Acylindrical Vshape but having `a'slight ltaper l23, and it is made concentric with member 9. vIf conductor 9 vdid vnot lharden into -place exactly -coaXia-l with recess 3, the walls 'of holder I will `not be of uniform thickness, but this is immaterial. The unit is Vnow placed in a tapered 'chuck which ts the taper formed on the unit, and a tip 3| is formed by turning down the end of the unit. This tip 3I is `also formed concentric with 'the outside of the 'unit a'nd'with conductor 9. An insulating tape having 'good Adielectric properties at the operating frequencies is now wound Aon the tapered portion, `as at `33, and the wound unit 4is then forced into a `mating taper in body which has `standard clamp adaptors 31 at each end whereby the 'completed unit may be connected to concentric transmission lines such as 38, 39. With Asuoli connection,

=conductor 9 'may slide over `the 'inner vconductor "40 of transmission line v38, as `at 4l, and tip 3l may slide into the inner conductor 42 of the other transmission Aline 39,'asat 43. It is obvious that either or both conductor 9 'and tip 3`I could slide over or lunder its corresponding connecting member.

The tape 33 forms'the dielectric of a'distributed capacitance whose electrodes are holder I and body 35. The capacitance acts as a distributed bypass condenser for the waves rectified by the crystal 1. Furthermore, the construction is such that all parts of the crystal circuit are fully shielded, since everything is within body 35 which acts as a continuation of the outer conductor 44 of transmission line 39. 'The output transmission line 39 may be replaced by an ordinary shielded cable if high frequency emciency is not necessary for the rectied currents.

The above is, of course, only one way of adapting the crystal holder I of the invention to a particular use. yThe method of mounting the crystal 1 above fdescribed may obviously be used to mount this crystal in an opening in any metallic body whatsoever, and is not restricted to the particular type shown. Successful crystal mountings have been made in the end of a 10-32 screw, and it is possible to make a mounting by the method `described in an opening as -small as .060 inch ldeep and .1050 inch wide.

The method of testing the -crystal for to Adetermine when the catfs-whisker -S -is in contact with a suitable sensitive spot will vnow be explained. Referring to Fig. 3, it will be seen that clamp i9 is insulated from base -I3 and bracket 45 as by an insulating block 41. Conductor 9 which is one termina-i fof crystal '1, is connected as through members I1 Aand clamp II9 and by mea-ns of a conductor 59, `to a resistor '49 which is connected in turn to one terminal of the secondary winding -of stepdown `trans-former -5I energized from Lan A. (C. supply line 53. The holder I, which acts as the other terminal of y'the -crystal 1, is connected, for example, through base I3 and bracket 45 and by means fofconduotor 6I to the other side of the secondary winding -of transformer 5I, 'which fis 4designed to .have `suitable seccndary voltage chosen so as 'to Yprevent any damage fto the crystal 1. Resistor 49 prevents excessive current from flowing in the crystal circuit. A standard-oscillograph is energized from the same supply line 53 through' -its usual power supply 51. AOne pair 'of deflecting plates of oscillograph 35:5, such Aas 'the 4horizontal deflectin'g plates, is connected across "resistor 49. The fot-her pair, such as 'the vertical defle'cting pla-tes, is connected across conductors -59 and GI which lare connected tothe crystal A1,1s'o that'this pair` is energized by the voltage across crystal 1. lThe usual amplifiers may be used for-amplifying the voltages applied to the fdeiiecting plates, lf desired. Ii conductors 59 and EI -were openrcircuited, the voltage across resistor 49 would be Zero and that across conductors 59, 6I would be maximum. -Accordinglly, fa trace 163 such as that shown in Fig. 4 would be obtained. If `conductors V59 and :6I were short-circuited, 'their potential diierence would be '-Zero, while vvthe voltageacross resistor 49 would be maximum so that the trace -65 `'shown in Fig. 5 would be obtained. It thus will be seen that'the cathode ray oscillog-raph trace indicates, byitsf's'lo'pe, the :impedance of the circuit connected to v'conductors 59, 31. 'A vertical trace 63, having 'infinite slope, indicates 'in- Afinite impedance 'Kopen-circuit). A 'horizontal trace 65, having 'zero slope, indicates zero impedance (short-circuit). Since Ahorizontal :deiiection is proportioned 'to current through -the 'crystal 1, and vertical deflection is proportional to voltage across crystal 1, the slope o'f the trace, which is therefore vproportional "to voltage `divided by current, will Valways v"indicate the true impedance of the crystal Atheoreticallyfperfect crystal should be a perfect short-circuit for half-cycles of applied A. C. of one polarity, and a perfect open-circuit for half -cycles of the other polarity, giving a trace 61 as shown in dotted lines in Fig. 6. Such a perfect trace 61 is rarely obtained. A good trace 69 often realized is shown in full lines in Fig. 6. Hence, in exploring the crystal 'l with the cats-Whisker 9, the latter is manipulated until a trace at least as good as 69 is obtained, and the cats Whisker 9 is then held in position until the thermoplastic material sets, thereby yielding a permanent crystal rectiiier or detector having the desirable qualities set forth above.

Although the invention has been illustrated by one embodiment, it is evident that many different embodiments of the invention could be made without departing from the scope thereof. It is therefore intended that the above description shall be interpreted as illustrative only, and not in a limiting sense.

Having described my invention, what I claim and desire to secure by Letters Patent is:

l. A concentric transmission line mounting for a crystal comprising a shielding outer conductor, an inner conducting body insulated from said outer conductor and having a cavity therein, a crystal tting snugly into the cavity so as to make intimate contact with' the Walls thereof, a Wire serving as a terminal for said crystal, and insulating material holding said wire in electrical contact with said crystal.

2. The method of making a mounted crystal which comprises the steps of forming a recess in a body of electrically conductive material, forming a bleeder hole at the bottom of said recess, forcing a unidirectionally conducting crystal into said recess to make intimate contact with the Walls of said recess, placing a thermoplastic substance in said recess, heating said body and substance above the temperature at which' said substance becomes plastic, whereby said substance Will iiow around said crystal and make intimate contact therewith, inserting a conductor into said plastic substance to make contact with said crystal, exploring the surface of said crystal until said conductor is in a position making contact with a sensitive spot of said crystal, holding said conductor in said position and simultaneously cooling said thermoplastic material to below its plasf tic temperature, whereby it solidiiies and holds said conductor permanently in said position.

3. A shielded crystal mounting comprising a roughly cylindrical body having a recess substantially concentric thereof, a unidirectionally conducting crystal pressed into said recess, a wire held in contact with said crystal roughly concentric of said body and a tubular member placed outside said body and insulated therefrom, whereby said wire and said ltubular member form input terminals to said crystal, said body and said tubular member form output terminals, and said body and tubular member form a by-pass condenser.

4. A device as claimed in claim 3 further comprising adapting means for connecting said input terminals to a concentric transmission line, and for connecting said output terminals to a shielded line.

5. A shielded crystal mounting comprising a conducting body having a recess therein, an unidirectionally conducting crystal seated within the recess in electrical contact with said body, a conducting member serving as a terminal for said crystal, and insulating material holding said conductor in electrical contact with said crystal, a tubular member placed outside said conducting body and means electrically insulating said member from said body whereby said conducting member and said tubular member form input terminals to said crystal, said conducting body and said tubular member form output terminals, and said body and said tubular member form a bypass condenser.

6. In a mounting for a unidirectional conducting crystal, a body of electrically conducting material formed with a recess in which said crystal is seated in intimate contact with said body, a conductor extending into said recess into Contact with a sensitive area of said crystal, solidiiied insulating means contained within said recess `for retaining said crystal therein and surrounding and retaining said conductor in contact with said crystal within said recess, and substantiallyraxially aligned connector terminals for said body and said conductor respectively projecting 'from opposite ends of said body.

7. In a mounting for a unidirectional conducting crystal, a member of electrically conducting material formed rwith a recess in which said crystal is seated in intimate contact with said member, a conductor extending into said recess into contact With a sensitive area of said crystal, solidied insulating means retaining said crystal in said recess and retaining said conductor` in contact with said crystal, a second member of conducting material extending about said rst member, and electrical insulation between said members.

8. A mounting for a unidirectional conducting crystal comprising a body of electrically conducting material formed with a recess in which said crystal is disposed in intimate contact with said body, a conductor in contact with a sensitive area of said crystal, insulating means securing said crystal to the walls of said recess and retaining said conductor in contact with said crystal, and substantially axially aligned connector terminals for said body and said conductor respectively projecting from opposite ends of said body.

FREDERICK L. SALISBURY. 

